1. Field of the Invention
This invention relates to heating vessels and in particular, to modifying the circulation of exhaust gas within a high temperature liquifying furnace.
2A. Technical Considerations
One type of glass melting process entails feeding glass batch materials onto a pool of molten glass contained within a tank-type melting furnace and applying thermal energy to melt the materials into the pool of molten glass. The melting tank conventionally contains a relatively large volume of molten glass so as to provide sufficient residence time for currents in the molten glass to effect some degree of homogenization before the glass is discharged to a forming operation. These recirculating flows in a tank type melter may result in inefficient use of thermal energy. Conventional overhead radiant heating is inefficient in that only a portion of its radiant heat is directed downward towards the material being melted.
As an alternative to tank type glass melting furnaces as described above, U.S. Pat. No. 4,381,934 to Kunkle and Matesa, which teachings are incorporated by reference, discloses an intensified batch liquefaction process in which large volumes of glass batch materials are efficiently liquefied in a relatively small liquefaction vessel. This type of process, particularly when using intensified heat sources such as oxygen-fuel burners, produces relatively small volumes of high temperature exhaust gases. The heat from this exhaust gas can be recovered and used to directly heat a batch stream feeding the liquefaction vessel so as to improve the overall efficiency of the process.
During the heating and melting process, it is believed that certain components of the batch material vaporize. These vapors may be corrosive and when combined with the hot exhaust gas stream that circulates through the vessels of the type disclosed in U.S. Pat. No. 4,381,934, may corrode exposed interior surfaces. In addition, the exhaust gas may entrain particulate matter within the vessel which may act as an abrasive to exposed interior surface.
An exhaust outlet on the lid of the vessel, for example, but limited to that disclosed in the two-stage batch liquefaction process as of U.S. Pat. No. 4,519,814 to Demarest, which teachings are incorporated by reference, may potentially lead to further process limitation due to the circulation of the hot exhaust gas in the vessel. Most of the exhaust gas must exit the vessel through the exhaust outlet. As as result there will be greater exhaust flow and corresponding wear. Furthermore, as pressure builds up within the vessel, the exhaust outlet provides a pressure relief outlet resulting in a high velocity exhausting of the exhaust gas. As a consequence, the vessel in the vicinity of the exhaust duct outlet may have increased wear when compared to the remaining exposed portions of the vessel. The potential wear problem may be particularly pronounced when the exhaust outlet is off center from the rotational centerline of the liquefaction vessel. The circulation of the exhaust gas within the vessel may be slowed in the direction of the exhaust outlet, establishing an asymmetric circulation within the vessel that may result in accelerated vessel wear at exposed portions. The problem may be complicated even further if the burners are positioned asymmetrically in the vessel so as to further distort the circulation pattern within the vessel.
It would be advantageous to control the exhaust gas circulation within the heating vessel so as to minimize the limitations discussed above.
2B. Patents of Interest
U.S. Pat. No. 2,006,947 to Ferguson teaches a centrifugal glass melting furnace with angularly adjustable burners. The furnace includes a steel shell with heat insulating liner mounted for rotation about a vertical axis. Burner openings in a stationery cover above the shell are directed obliquely outward from the axis of rotation of the rotating furnace vessel so that flames from the burners strike batch material on the insulating liner of the steel shell. The burners are oriented to direct their flame generally in the direction of rotation of the furnace.
U.S. Pat. No. 2,834,157 to Bowes teaches a glass melting furnace having an inverted frusto-conical hearth. A cover is supported over the hearth such that the hearth can rotate under the cover. The cover includes a plurality of spaced apertures for insertion of fuel nozzles which direct flames into the interior of the furnace. The flames follow a generally tangential path with respect to the walls of the furnace.
None of the cited art recognizes or discusses the problems that can occur in these types of systems such as particle entrainment in exhaust gas and accelerated wear of the furnace.